REPORT ON THE PHYSIOLOGY OF THE NERVOUS SYSTEM. 79 



This organ may now be regarded as mainly, if not solely, a 

 medium of intercourse between the external world and the brain, 

 and again between the brain and the voluntary muscles, its two 

 anterior columns being subservient to motion, its two posterior 

 to sensation. In the present state of our knowledge it would 

 be fruitless to try to penetrate into the minute philosophy of 

 these actions : but it seems probable, from recent discoveries 

 on the ultimate anatomy of tissue, that these actions are mole- 

 cular, having their place in the globular elements, into which all 

 living textures are resolvable by microscopic analysis ; — that 

 the physical changes, e. g. impressed by external objects on the 

 delicate net-work of nerve which invests the tegumentary mem- 

 branes and open cavities, are propagated thence, from particle 

 to particle, along the continuous filaments, to their origins in the 

 posterior spinal columns, and thence to the central point, where 

 they become objects of perception; — and that the motive sti- 

 mulus of volition is similarly transmitted down the anterior co- 

 lumns and nerves, to the organs of locomotion. Indeed, it is a 

 legitimate inference from Sir Charles Bell's discoveries, that a 

 simple nervous filament, or medullary column, can only propa- 

 gate an impression in one line of direction, viz. either towards 

 or from the central seat of perception and of will ; and this cu- 

 rious law of nervous actions would seem to point at some in- 

 sensible molecular motion as their essential condition. 



It remains to investigate the arguments which have been 

 supposed to prove the residence in the spinal marrow of the 

 power of originating and controlling the actions of the heart. 

 This question has been matter of eager controversy, from its 

 bearing vipon the general relations of nerve and muscle. With- 

 out prejudging this latter topic, it may simplify its future con- 

 sideration, and will at the same time be more consistent with 

 strict arrangement, to state here merely the facts which have 

 reference to the spinal medulla. 



The woi'k of Legallois, entitled ^^ Experiences sur le Prin- 

 cipe de la Vie, notamment sur celni des Mouvemens du Cceur 

 et si/r le Siege de ce Principe* ," was the first remarkable essay 

 on the relations between the heart and the spinal cord. It will, 

 however, be sufficient to allude in general terms to the conclu- 

 sions of Legallois, since they have been entirely subverted by 

 the subsequent researches of Dr. Wilson Philip and M. Flou- 

 rens. Legallois's main doctrine was, that the principle which 

 animates each part of the body resides in that part of the spinal 

 medulla whence its nerves have their origin; and that it is also 



• CEuvres de Legallois, torn. i. pp. 97, 99, &c. 



